Most RTL-SDR dongles below $20 come with a small black mount and short antenna; here're a few easy mods to make them better for radio signal reception.
1. Place magnetic mount on a metal surface
Food tin cans, pans, as long as the mount "snaps" to it, will do the job.
2. Replace short black fixed antenna with piece of wire
Screw off the black antenna, wrap some wire around the screw, fix it in place with tape or leave it as is.
Electrical cord wire, or any other type with lots of small wires, not just a few big ones, are much easier to use.
Length of wire depends on frequency of interest; divide 75 by MHz number to get result in meters.
For example, for airband, the math is 75/125=0.6m, which is 24 inches, or two foot. Or elbow to fingertip length for me.
The intenna above will reliably receive higher MHz number frequencies as well.
3. Extend antenna cable
All dongles I came across (except the SMArt) ship with 3 feet / 1m long cable, which is simply too short. Antenna should be outside, and cable often doesn't reach.
Cut the cable, splice some coax inbetween the two ends, done. Coax costs little money and available everywhere.
4. Remove IR receiver and LED light
This will probably invalidate your warranty.
RTL-SDR dongles are originally TV tuners - if you got a remote with it, it will have an IR receiver inside, which is not necessary for radio signal reception.
The majority of dongles also have a LED light. This increases power use, if you fancy the Christmas tree effect, leave it in peace.
Remove both by gently moving them back and forth, eventually they will snap off.
If you have a smaller dongle, the LED light might be non-removable, but the IR receiver is almost always removable:
5. Place dongle in a metal tin.
This will significantly reduce interference from nearby radio sources, like WiFi and brooadcast FM radio.
I use a sweet tin in the image, anything will do as long as it's made from metal.